Liverpool may have a big part to play in helping their old rivals Manchester United sign their long-term defensive target Mats Hummels from Borussia Dortmund.

The German World Cup winner has been consistently linked with a move to Old Trafford, but Dortmund boss Jurgen Klopp seemingly ruled out a possible switch recently, per the Guardian:

What are we talking about today? Mats to Manchester United? For how much? €20 million (£15.8million)? With those kind of sums can you forget that straight away.

However, according to David Kent in the Daily Mail, the move could be revived depending on the movements of various Liverpool players:

Manchester United are hoping a deal for Borussia Dortmund's Mats Hummels can be revived with Dortmund now looking at Liverpool's Portuguese centre-back Tiago Ilori.

Dortmund have asked to take the 21-year-old Ilori on loan as a possible replacement should a fee be agreed with United on the Germany international Hummels.

Dortmund are reportedly interested in bringing Liverpool's young defender to the Bundesliga having been impressed during his loan spell at Granada last season.

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His arrival—along with Dortmund's recent purchase of Matthias Ginter—would pave the way for Hummels' exit, as Klopp's side would be somewhat centre-back heavy considering the continued presence of Neven Subotic and Sokratis Papastathopoulos.

Furthermore, Barcelona—long rumoured, per Kent's report, as United's main rivals to snap up Hummels—are close to an agreement to sign Reds centre-back Daniel Agger, per beIN Sports' Tancredi Palmeri:

If the La Liga giants do complete the deal for the Danish 29-year-old, they will likely no longer be interested in Hummels, having also recently signed Jeremy Mathieu from Valencia.

Kent's report suggests United are prepared to offer £30 million for Hummels' services, a figure that may finally persuade Dortmund to part with the 25-year-old.

United must be prepared to spend big on bolstering their back line as stalwart centre-back duo Nemanja Vidic and Rio Ferdinand have both departed, leaving them short in central defence.

Hummels would be the ideal replacement, his combination of aggression, authority and technique exactly what is needed in a suspect Red Devils defence, per football journalist Tom McDermott:

However, Hummels' arrival at Old Trafford still seems highly unlikely given the denials of any possible move by both Klopp and the player's father, an idea backed up by Sky Germany's Jan Aage Fjortoft:

United boss Louis Van Gaal will likely have to look elsewhere for quality centre-backs, a long-rumoured move for Arsenal's Thomas Vermaelen looking the best possible alternative.

The Belgian's Premier League experience is a definite plus, and although he is not quite on the level of Hummels, he would be a fine addition to United's squad.

The Hummels-to-United saga has seemingly gone on all summer and is likely to end in vain for the Manchester outfit, although there is still a slight chance that Liverpool could do them a huge favour with the movement of their players.